An axial image, a sagittal image, or a coronal image, which are cone-beam-reconstructed by a CT apparatus, are displayed on a CRT monitor in an image display apparatus.
In a conventional image display apparatus, for instance, while only an axial image is stored in a magnetic disk, when the axial image is displayed, the axial image is read out from the magnetic disk to be displayed, whereas when a sagittal image and a coronal image are displayed, these sagittal and coronal images are reconstructed based upon the saved axial image to display the reconstructed sagittal/coronal images.
However, in the conventional image display apparatus, since a very large number of axial images are obtained by way of the cone-beam reconstruction, there is such a problem that while this very large number of axial images, and both the sagittal images and the coronal images which are obtained from the axial images are displayed on the monitor, searching of a desirable diagnostic portion may constitute very hard works with respect to operators.
Also, in order to form one sheet of such a sagittal image and one sheet of such a coronal image, all of the axial images are necessarily required. Thus, there is another problem that lengthy time is required so as to read out all of these axial images from the magnetic disk and to load the read axial images on the main memory.
To shorten the above-described readout time, such a method is conceivable. That is, while all of the three sorts of images are formed and the formed images are saved in the magnetic disk, only such an image to be displayed may be read out. However, this conceivable method requires the storage capacity of the magnetic disk which is three times larger than that of the above-explained method, resulting in a not-preferable method.
Also, there is such a need that an operator designates an effective region of data of a three-dimensional image so as to reduce an amount of data to be processed. As a result, the operator wants to display the images in a high speed.
Also, when an image is displayed, it is not easy to selectively determine that which image among the above-explained three sorts of images is displayed.